The present invention relates to methods and devices for assaying biological fluid samples. More particularly, the invention relates to methods and devices for detecting multiple analytes in fluid sample while also determining whether the condition of the sample has been altered or degraded.
In their most simple form, chromatographic analyte analyte test strips permit an assay to be performed in a single step (application of an analyte sample to the device) to produce visually observable assay results (such as those indicated by colored bars on the analyte test strip). However, a common limitation of such analyte test strips is that they can only be used to detect a single analyte, requiring that serial assay procedures be performed to detect additional analytes (for example, to test a sample for the presence of a panel of narcotics). Multiple dipping steps, such as are commonly used when multiple dipstick assays are separately performed, present not only a possible loss of sensitivity of the assay (through reagent mixing or loss of reagent solutions), but also an esthetic and hygienic problem for the analyst. Repetitive performance of assay procedures is also tedious, which increases the risk that assays will be performed improperly or the results misinterpreted.
A further limitation on the accuracy of analyte assays is the potential for adulteration or degradation of the analyte sample prior to performance of the assay. This is an especially acute problem in assays for drugs of abuse in urine, where test subjects are often motivated to creatively alter the composition of the urine sample to produce falsely negative assay results.
The present invention provides an assay device, device for separating a fluid analyte sample for use in multiple assay procedures and methods for performing multiple analyte assays while contemporaneously evaluating whether the analyte sample has been adulterated or otherwise compromised.
To the latter end, the invention provides assay devices which include an assay sample integrity monitoring system. The system consists of a pad in which determinants are provided which allow for measurement of parameters indicative of the condition of a fluid analyte sample, such as specific gravity and pH. The pad is in fluid communication with a carrier membrane, through which analyte sample flows without contacting the analyte analyte test strips of the device.
Analyte sample fluid is added to the device and becomes divided between the carrier membrane and the analyte test strips, thus allowing for contemporaneous measurement of both analytes and adulterants or other compromising elements in the analyte sample. The separation of the analyte sample between the carrier membrane and the analyte test strips avoids the possibility of contamination of the sample by analyte test strip reagents which might affect the sample integrity determination.
In one embodiment of the assay device, the assay device is a dipstick having multiple analyte test strips, each of which includes a test zone and a control zone. The analyte test strips are enclosed in a housing having an open side through which an end of each analyte test strip protrudes to form a sample loading zone. A protective cap is provided to seal the protruding ends of the analyte test strips from exposure while not in use. Each analyte test strip is separated from the next within the housing by a raised spacer. The portion of the housing which overlies the test and control zones is transparent to permit visually observible results shown in each zone to be viewed.
In cassette form, the assay device has the same structure described above, but the protruding analyte test strips are inserted into a cap which has a sample port for application of sample to the analyte test strips. The cap is retained on the assay device by a close fit over the device housing.
In either its dipstick or cassette form, the sample integrity monitoring system works in parallel with the analyte test strips of the devices of the invention. In particular, the carrier membrane can occupy the same slot in the device base as the analyte test strip, and will include a fluid migration barrier between the analyte test strip and the integrity determinant pad, or can occupy separate slots in the base.
Each analyte test strip provides binders and assay reagents for detection of a different analyte in the sample fluid. In a particularly preferred embodiment of the assay device, the housing may be opened to permit substitution of different analyte test strips to allow each device to be customized for detection of specific analytes of interest.
The invention also provides a separator device for dividing a fluid assay analyte sample into portions for use in multiple assays without need for contact between the assay operator and the fluid sample. This latter feature of the device increases operator safety and avoids inadvertent contamination of the assay sample. The separator device may be used to separate any fluid assay sample, but is especially useful in assaying samples for the presence of narcotics, where a positive result on first testing of the sample may necessarily be followed by additional testing of the sample to confirm the result and the identity of the detected narcotic. To this end, the separator device is adapted particularly well to use with the assay device of this invention.
The assay device of the invention makes specimen analysis easier and increases its accuracy because an analyte sample need only to be applied once to the assay device for testing and can, in the same step, be evaluated for potential adulteration or compromise. In addition, the replaceable nature of the analyte test strips and integrity monitoring system allows the analyst to customize the array of assays and integrity monitoring system determinants to the testing situation. Because the customization can be performed before adding the test sample (e.g., urine), fewer manipulations with the analyte sample are needed to obtain the desired information. In addition, use of the separator device permits further testing of the sample to be performed without risk of adulterating the sample in a preliminary assay performed according to the invention.
The invention also provides a method for assaying one or more analytes of interest. The protruding ends of the device are dipped into a fluid analyte sample. Binding of an analyte present in the sample with one or more specific ligands causes formation of specific visual pattern in the test and control zones indicative of the test result. In addition, passage of the sample into the sample integrity monitoring system also produced visual results (which vary depending on the parameters evaluated), thereby enabling the assay operator to immediately determine whether the sample appears to be adulterated or otherwise compromised.
The assay results performed according to the invention may be read visually without use of separate measuring equipment. Thus, performance of assays according to the invention requires only that the user introduce the requisite amount of test sample into the device of the invention, then observe any color changes which appear shortly thereafter in a detection zone of an analyte strip. The method of the invention is especially useful for screening fluid analyte samples (e.g., urine) for the presence or absence of drugs of abuse.